As already discussed, the diameter of the connecting tube, however, should not be made less than 0.012 cm, (0.005 in. I. D.), not because of the pressure drop that will occur across it, but because tubes of less diameter will easily become blocked. Employing equation (12) the volume variance and the volume standard deviation contribution from connecting tubes of different lengths can be calculated and the results are shown in figure 9A and 9B. The tube radius is assumed to be 0.012 cm, the flow rate 1 ml per minute, and the diffusivity of the solute in the mobile phase 2.5 x 10^-5 cm²/sec.

Figure 9 The Volume Variance and the Volume Standard Deviation Contribution from Connecting Tubes of Different Lengths